Field of the Invention
The present invention relates to a method of manufacturing a clutch housing used for a vehicle transmission or the like.
Description of the Related Art
In general, there has been used a drum type clutch housing for an automatic transmission (AT) for an automobile or the like. A clutch housing as mentioned above has been manufactured by cold forging with a predetermined degree of accuracy and in predetermined dimensions.
In general, the clutch housing is composed of a center boss portion, and a drum portion joined to the former. The boss portion and the drum portion are joined to each other, firmly by welding and calking. As shown in FIGS. 10 and 11, a housing 10 is composed of a boss member 11 and a drum portion 12 which are joined to each other by electron beam welding. It is noted here that the boss member 11 is made of a material which requires refining in view of a required function and a required strength. Further, the drum portion 12 is made of a material having an appropriately selected degree of harness in view of its plastic workability, but has not to have a high degree of hardness. FIG. 10 shows the boss portion 11 which is extended inward of the housing 10, but FIG. 11 shows the boss portion is extended outward from the housing 10.
Further, there has been known a manufacturing method in which a clutch housing is previously by hot forging in a product-like form, and thereafter, and is then subjected to cold forging so as to ensure a desired degree of accuracy (Refer to, for example, Japanese Patent Laid-Open No. H03-189044). In this example, the boss portion and the drum portion are integrally provided with each other. In a method of manufacturing an integral type clutch drum with a hub, which is composed of a boss portion and a drum portion tooth-formed by forging, the boss portion which requires a predetermined strength is heat-treated in order to obtain a predetermined degree of hardness.
The clutch housings as stated above have caused the following problems:
Conventional integral type clutch housings have been refined in its entirely including the drum portion, and accordingly, there has been caused such a problem that the refining deteriorates the workability.
Further, since the hardness of the drum portion is increased, similar to the boss portion, the hardness of the drum portion is too hard to carry out plastic tooth-formation, resulting in occurrence of deficiencies such as material clacking during working, a shortened serviced life of a working jig or vibration of working machinery due to strong plastic deformation and the like. Further, since the boss portion has to be heat-treated after the plastic tooth formation, there has been raised such a disadvantage that deformation is caused after plastic working of the drum portion, and so forth.